The present invention relates to a test leak unit comprising a supply of test gas, preferably helium, and an element for determining leakage rates.
In leak testing of hollow bodies, the method of vacuum test gas leakage detection has prevailed. The wall of the hollow body is exposed to a differential1) pressure produced by evacuating the hollow body or its surroundings. Test gas, commonly helium, admitted on the side at the higher pressure, penetrates possibly present leaks and is recorded by a test gas detector, for example, a mass spectrometer, connected on the side at the lower pressure.
1) Translator""s note: xe2x80x9cThe German text states xe2x80x9cDifferendruckxe2x80x9d here whereas xe2x80x9cDifferenzdruckxe2x80x9d would be appropriate. Therefore xe2x80x9cDifferenzdruckxe2x80x9d has been assumed for the translation. 
Test leak units of the aforementioned kind are, for example, known from DE-A documents 32 43 752 and 36 13 694. These supply a leakage of known properties and serve the purpose of calibrating leak searching instruments. To this end, they are connected via connecting lines to the leak searching instrument in which a test gas detector is located.
Frequently, such test leak units are built into the leak searching instrument. An other possibility of checking the operation of the leak searching instrument is to hold the test leak unit with its opening, through which the test gas flows out via a leakage rate determining element, in the vicinity of the inlet of the leak searching instrument. The test gas arriving at the test gas detector will then produce the desired test signals.
From WO 98/16809 a process and a device for testing the leak tightness of packages is known. Located within the sealed package is the test gas (preferably helium, also nitrogen, argon, carbon monoxide, halogen gases or the like). The leakage test is performed within a test chamber consisting of foils. For a process and a device of this kind, a test step has already been proposed improving the reliability of the leakage test. This proposal is such that the wall of a unit under test is provided with a leak and that the leak searching process be done with this unit under test itself. Thus one of the units under test itself is being used as the test leak unit. However, checking of a leak searching instrument with a xe2x80x9cquasi test leakxe2x80x9d of this kind is only possible qualitatively. The magnitude of the leakage produced by piercing is unknown. This equally applied to the concentration of the test gas within the unit under test, which above all may have changed, if the selected unit under test for the xe2x80x9cquasi test leakxe2x80x9d already had a leakage before.
It is the task of the present invention to create a simple, robust, and easily refilled test leak unit which is also suited for packaging leak searching instruments.
This task is solved by the present invention in the case of a test leak unit of the aforementioned kind, by storing the test gas reservoir substantially under atmospheric pressure in a resealable reservoir with a closing part, where with the reservoir sealed, test gas tight sealing means are provided between closing part and reservoir and where the leakage rate determining element forms part of the closing part.
Since the pressure in the test gas reservoir is approximately at atmospheric pressure, test gas flows out through the leakage rate determining element only when the test leak unit is placed in a vacuum chamber, i.e. in a leak searching chamber in which the units under test are subjected to a vacuum leakage test. Without a significant change in the concentration of the test gas in the reservoir, many test cycles (for a reservoir of 0.25 liters and helium as the test gas about 10,000) can be run. The fact that the filling pressure in the test leak unit corresponds to the surrounding atmospheric pressure, offers the added benefit that refilling the test leak unit may be performed simply with the aid of a spray gun. An otherwise necessary gas lock is no longer required. Spraying of the test gas into the reservoir has the effect of causing the previously used filling to flow out. In all, relatively large leakage rates may be attained with the test leak unit according to the present invention over a long period of time. In the case of the otherwise common internal pressure far above atmospheric pressure of known test leak units, the reduction in pressure will rapidly cause a change in the leakage rate.
The adaptation of the leakage rate of the test leak unit according to the present invention to the specific process of the customer, may be simply performed by selecting a closing part with the desired leakage rate. If the specific requirements of the customer change, this closing part may be exchanged quickly and simply by a closing part having a different leakage rate.
It is important, that when employing a test leak unit according to the present invention in the vacuum of a leak searching chamber, the test gas will flow out exclusively through the leakage rate determining element. Any further seal, be it the seal between closing part and reservoir or a seal between the leakage rate determining element and the closing part, must provide a tight seal against the test gas. When employing helium as the test gas, PU seals must be used, preferably xe2x80x9cPlatilonxe2x80x9d (company Atochem, Bonn).
A screwed plug preferably serves as the seal between closing part and reservoir. Compared to other closing means (bayonet catch, for example) the desired level of leak tightness against the test gas can be attained particularly well.